This invention is in the field of plastic cutting machinery. More particularly, it is an apparatus for cutting tear-off strips from a strip of plastic whose width is equal to the length of the tear-off strip and for applying the tear-off strips to a piece of packaging material. The apparatus has one movable and one stationary straight knife for the progressive cutting of the tear-off strips. A device to which suction can be applied transfers the tear-off strip along its longitudinal direction to a suction roll rotating at the same speed as the packaging material is moving. The suction roll picks up and is partially wrapped about by the continuously conveyed packaging material. The tear-off strip is also picked up by the suction roll and overlays the packaging material. A welding device welds the tear-off strip to the web of packaging material.
German reference DE-B-1,167,731 shows the use of one stationary and one movable knife in an apparatus for cutting off and applying tear-off strips. The knives are arranged at a slight angle to one another, in order to produce a "pulling" cut. The movable knife may have suction air applied to it, in which case the knife transfers the cut tear-off strip, held in place by the suction air, to a guide shoe which may also have suction air applied to it. The tear-off strip projects beyond the guide shoe so that it can be picked up by a continuously rotating drum, the drum also having suction air. A web of packaging material, to which the tear-off strip will be welded, is also held by the drum. With high packaging rates and a fast rotating drum, the tear-off strips cut by this apparatus cannot be reliably picked up. There is a risk that the cut tear-off strip will remain in the guide shoe and jam the entire apparatus, as the next cut tear-off strips cannot be held by the guide shoe, until the previously cut strip has been removed from the vacuum holes in the rotating drum. German Reference DE-B-1,249,067 also shows an apparatus for cutting a tear-off strip. Two knives bent in the form of an arc are used, resulting in a "striking" cut. In this machine the tear-off strip is cut from a web of tear-off strips and is transferred directly to a suction roll which is partially wrapped by a web of packaging material.
The apparatus shown in DE-A-1,586,120 has the tear-off strips being applied transversely to the conveying direction of the packaging material. The conveying takes place using a multi-knife roll and the aid of suction air. In this case the tear-off strips are self-adhesive and can simply be pressed onto the web of packaging material, without having to be further transported.
In German Reference DE-A-3,423,295, a knife arrangement with the knives being arranged obliquely with respect to the transport path of the web of packaging material is shown. The movable knife, which holds a cut tear-off strip by means of suction air, can be pivoted out of the cutting position into a position above the web of packaging material, and can deposit the cut-off tear-off strip onto it. During further transport the tear-off strip is welded to the web of packaging material. A relatively large range of motion is required by the movable knife, which restricts the cycle rates, as relatively large masses are moved. Additionally, adjustment is complicated and the tear-off strip is not guided after being deposited onto the web of packaging material, which means that it can go astray. Also, the web of packaging material has to be conveyed intermittently, as the tear-off strip cannot be deposited on a moving web of packaging material.